The present invention relates to stable, aqueous coating compositions. In particular the invention relates to an improved stable aqueous coating composition containing as the primary coating agent an alkali soluble resin of low molecular weight and high acid number and aqueous ammonia sufficient to provide a pH no less than about 9.0.
In the protective coating field, such as temporary organic coatings, including certain floor coatings, it is desirable to have minimum carboxyl functionality present in order to avoid the solubilizing and spotting effects normally obtained when water is brought into contact with such coating. However, the hardness, durability, gloss, and removability properties of these films are effected by the degree of carboxyl functionality present. Therefore, most coating compositions developed heretofore, represent a compromise with respect to properties such as hardness, durability, gloss, removability, and resistance.
It has been found that various organic films containing carboxyl functionality sufficient to obtain easy removal, tend, upon aging, to undergo a degrading effect; that is a loss of functionality which renders the carboxyl groups substantially unavailable. This degrading effect produces films which are difficult to remove by means of conventional film remover substances, such as detergents, and results in film buildup. Film buildup is usually accompanied by degradation in color, for example, yellowing, and eventually necessitates complete film removal with high caustic solutions or solutions containing organic solvents or by various abrasive methods, all of which have been found to effect the substrate adversely.
The problem of removability, degradation and film buildup was alleviated greatly by the use of the metal cross-linked polymers disclosed in U.S. Pat. Nos. 3,308,078 and 3,320,196. The metal complex salts disclosed in the above patents form temporary bonds or cross-links between adjacent polymer carboxyl functional groups so as to retard their exposure and subsequent degradation. These floor coating compositions provided films with good gloss and strength which could be easily removed by cleaning with detergent and ammonia but are water insensitive and detergent resistant under normal conditions.
For many applications, among them the home, it has been deemed desirable to maintain highly polished floor surfaces for aesthetic appeal as well as for other reasons. In lieu of detergent-cleaning a yellowed or dirty floor film, it is considered highly desirable to merely recoat and thereby simultaneously clean and remove the old polish layer and form a new film. Accordingly, the need has arisen for a self-stripping floor polish adapted to be frequently reapplied to maintain a highly polished substrate which is not to be washed with detergent between applications. The polish must have non-yellowing characteristics and be shelf-stable.
Recently, various innovations have been introduced permitting a dried floor coating to be simultaneously cleaned and polished without the need for conventional washing and repolishing, and without film buildup. As illustrated in U.S. Pat. No. 3,308,078 modifications in the above type of formulation can produce a stable, aqueous coating composition which provide metal-containing organic films having unique structural integrity; captive functional groups which are not easily degraded; controlled removability and high gloss, hardness and durability. These coatings are designated as self-sensitive coatings and after application are resistant to detergent washing and can be removed by recoating. Upon recoating, a portion of the dried film is dispersed in the fresh coating and a new coating is provided which is substantially free from the heel marks, scuffs, and other dirt contained in the old dried coating.
The stable self-stripping aqueous floor coating composition of the present invention comprises as the primary coating agent a solution of an alkali soluble resin having a weight average molecular weight of from about 500 to about 40,000 and an acid number within the range of from 120 to 550. This alkali soluble resin is an addition resin containing at least two ethylenically unsaturated monomers, one of these monomers being a ligand-free monomer while the other monomer contains carboxyl functional groups. The coating composition of the present invention also includes aqueous ammonia in a concentration sufficient to provide a pH of no less than about 9.0 and a combined amount of wax, solvent, leveling agent, surfactant and high molecular weight polymer equal to or greater than 9% by weight of the resin. This composition is readily adapted to disperse a previously deposited dried coating composition of itself and replace the dried coating with a fresh coating having even gloss and durability.